Conventionally, a variety of acid catalysts are used for a variety of chemical reactions such as esterification, hydrolysis, alkylation, dehydration condensation of alcohols, and hydration of olefins, and sulfuric acid is widely used as an acid catalyst in the chemical industry and other industries. Sulfuric acid is used in large amounts due to its low price. However, sulfuric acid, which is a liquid, has a problem in that a large amount of energy is required in the process of separating, recovering, purifying, and recycling sulfuric acid from products after reactions, the process of neutralizing residual sulfuric acid in products, the process of removing the salt produced by the neutralization, the wastewater treatment process, and other processes.
On the other hand, solid acid catalysts have also come to be used as alternatives to liquid acid catalysts such as sulfuric acid, because they can be more easily separated, recovered, and used repeatedly than liquid acids such as sulfuric acid.
Typical solid acid catalysts being used include silica-alumina, zeolite, and the like. However, these solid acid catalysts decrease in catalytic activity when used, for example, in water, and therefore are difficult to use industrially as alternatives to sulfuric acid.
In recent years, carbon-based solid acids having sulfonic acid groups introduced into carbonaceous materials have been developed as solid acid catalysts capable of being used even in water.
Concerning carbon-based solid acids having sulfonic acid groups introduced into carbonaceous materials, for example, Patent Document 1 discloses solid acids obtained by heating polycyclic aromatic hydrocarbons with concentrated or fuming sulfuric acid to condense and sulfonate the polycyclic aromatic hydrocarbons. For example, Patent Document 2 discloses a solid acid catalyst including a sulfonic acid group-containing carbonaceous material obtained by carbonizing and sulfonating phenolic resin. For example, Patent Document 3 discloses a solid acid obtained by partially carbonizing glucose, cellulose, or the like and then introducing sulfonic acid groups into the resulting amorphous carbon material.
However, these carbon-based solid acids have a problem in that they have insufficient catalytic activity or can easily decrease in catalytic activity when used repeatedly. Under such circumstances, there has been a demand for the development of a novel carbon-based solid acid that has high catalytic activity and resists degradation of its catalytic activity even when used repeatedly.